Electrical stimulation of the spinal cord or peripheral nerves can result in pain reduction and/or elimination. Medical leads having electrodes are often implanted near the spinal column to provide pain relief for chronic intractable pain. The electrodes stimulate tissue within the spinal column to reduce pain sensations at other parts of the body. The stimulation signals applied can be optimized for pain reduction or elimination depending on the location of the pain.
The area of excitation and the intensity of excitation vary according to the stimulation signals. To vary the area of excitation, an array of electrodes implanted near nerve tissue can be configured for a positive, negative, or neutral polarity such that the desired area within the spinal column is electrically stimulated. In addition, the stimulation signal applied on those implanted electrodes can be varied for a corresponding variation in area of excitation within the spinal column and in the intensity of excitation at the pain site.
Prior art electrodes are usually arrayed in a percutaneous or paddle lead. Presently, a percutaneous lead has certain advantages regarding ease of insertion over a paddle lead. However, because of present designs, electrical stimulation with a percutaneous lead occurs 360 degrees around the lead, thereby stimulating posterior portions of the epidural area as well the spinal area and hence, increases unnecessary power consumption.
Paddle leads on the other hand tend to focus the electrical field in only a 180-degree direction in the forward or anterior direction. Because of the electrical field being focused mainly in a single direction, less power is often needed using paddle leads.
Current lead designs suffer in that they often move axially, radially and/or longitudinally in the epidural space after insertion. A cross section of the epidural space can be considered to be an approximate of an isosceles triangular shape with the posterior angle being greater 90 degrees. Additionally, the two “equal angles” tend to drift downwards more anteriorally towards the spinal cord creating a “gutter” effect on the sides of the epidural space, as can be seen in FIG. 3.
Present leads fail to take advantage of the shape of the epidural space. Thus, especially in the case of percutaneous leads, they tend to drift into the side pockets or “gutters” of the epidural space rather than remaining near the centerline. This causes several undesirable effects such as causing greater power consumption in trying to stimulate nerves located near the centerline. Additionally, an unwanted effect of stimulating the nerve root may occur.
Certain paddle leads, such as that described in U.S. patent application Ser. No. 10/025,112, present a curved shaped to match the shape of the dura mater. However, these and other paddle lead designs fail in that their designs do not account for the shape of the epidural space as described above. Hence, they may drift towards one of either gutters and not align a lead in the epidural space. Other limitations in this and other designs will become evident in the detailed discussion of the invention.
What is needed is a lead whose design ensures proper axial placement and thereby maximizes nerve stimulation and minimizes power consumption.